1. Field of the Invention
The present general inventive concept relates to an inkjet ink composition and a multi-color inkjet ink set having the same, and more particularly, to an inkjet composition in which a transparency and a clarity of a photo image that is printed using the inkjet ink composition are improved simultaneously with an optimization of a stability and flowing properties of the inkjet ink composition, and in which a water resistance is reinforced by improving a fusing property of the inkjet ink composition, and a multi-color inkjet ink set having the same.
2. Description of the Related Art
An inkjet recording apparatus displays an image on a medium by ejecting ink droplets through a nozzle. An inkjet ink should have excellent drying properties in a medium, should not cause image bleeding, should display uniform images regardless of a medium type, should not cause color bleeding at an interface between different colors when printing multi-colored images, and should have excellent durability (i.e., water resistance, light resistance, and rubbing resistance). Various attempts have been made to provide a multi-color inkjet ink set including at least two ink compositions that satisfy such requirements.
For example, U.S. Pat. No. 4,849,770 employs a reactive dye or a reactive dispersant dye to improve a fusing of a dye on a fabric, and U.S. Pat. No. 5,631,309 employs a polymer that can perform a decarboxylation reaction with an oil-soluble dye or a dispersant dye, thereby improving water resistance of an image. U.S. Pat. No. 5,631,309 describes that storage stability can be improved by preventing ink from fusing on an inkjet head through the decarboxylation of the polymer. U.S. Pat. No. 6,033,463 describes that a fusing of ink on a paper can be accelerated and a water resistance of an image can be enhanced by using a dye having a solubility of less than 10% when selecting a main dye constituting a color ink, as well as by controlling a surface tension of a black ink and a color ink in an ink set including a pigment black ink and a dye color ink. In addition, U.S. Pat. No. 6,536,893 describes that a water resistance is enhanced since a dispersant dye or a subliming dye is sublimed by heat and pressure, recrystallized on a medium, and then solidified into a water-insoluble dye.
However, the above-described conventional solvent and dispersant dyes have little or no solubility in water. Accordingly, when such dyes are used in a conventional water-soluble ink, a small percentage of up to 20% by weight of a polymer is used in order to enhance a dispersibility or miscibility of the conventional ink. However, since a viscosity of such a conventional ink is too high, the conventional ink does not flow smoothly in an inkjet cartridge and thus the conventional ink is not ejected uniformly. Accordingly, such a conventional ink cannot maintain ink droplet uniformity or ejection uniformity in high speed-and-quality printers realizing high frequency and several pl (picoliters) of small droplets. Also, since Brownian motion can occur easily due to the presence of a large amount of the added polymer, the conventional ink including the polymer may become thick, thereby decreasing a stability of the conventional ink, and a printed image can also lose a transparency and clarity of the dye ink due to the large amount of the polymer. Accordingly, an appropriate selection of a concentration of the polymer becomes important when using the conventional solvent or dispersant dyes.
On the other hand, when using a dye that is easily soluble in water in an ink, a stability of the ink is excellent due to the good solubility of the dye in water, but printed images can be easily dissolved in water, and thus a water resistance of the ink is low. As a result, bleeding between colors occurs due to a movement of ink droplets on media on which the printed images are printed. Accordingly, an ether penetrant is conventionally used in excessive amounts to accelerate a fusing of the ink in order to enhance the weak water resistance and reduce the bleeding of the ink. However, an image quality is quickly decreased and the bleeding of the ink also deteriorates since the ink does not stay at an upper layer of the media.
Thus, in an ink including a dye having a solubility of less than 10%, a concentration of the dye in the ink is increased from an initial concentration thereof due to an evaporation of water in the ink when the ink is stored in a storage container for a long period or the cartridge is used for a long period. An amount of the dye in the ink after evaporation can be more than 10% according to the initial concentration of the dye used in preparing the ink. Thus, since the dye is precipitated as a solid, the ink cannot be used due to a decreased stability of the ink, or cannot be ejected due to a clogging of the ink in the cartridge. Therefore, it is required that a solubility of a dye be optimized in consideration of a correlation with a concentration of the dye used in an ink.